Photoreceptors and bipolar cells of the retina and hair cells of the auditory and vestibular systems signal sensory stimuli as graded changes in neurotransmitter release. To do so, these cells have evolved synaptic ribbons, proteinaceous structures that tether large numbers of synaptic vesicles near release sites. The molecular machinery underlying synaptic ribbon function is poorly understood. A handful of proteins have been localized to the synaptic ribbon and the importance of these individual molecules as well as how they contribute to the unique functions of the synaptic ribbon remains elusive. Of these proteins, the most abundant is Ribeye, a protein unique to the synaptic ribbon and thought to constitute most of the synaptic ribbon and hypothesized to form the core of the synaptic ribbon. Ribeye arises from an alternative start site of the transcriptional corepressor CtBP2. The precise role of Ribeye remains unknown and the long-term goal of this proposal is to determine the functional role of Ribeye in the synaptic ribbon. To study Ribeye function, we will employ a combination of molecular biology, genetic and electrophysiology primarily using zebrafish as a primary model system. In Aim 1 we generated and characterize zebrafish with targeted mutations in both ribeye genes. In Aim 2, we the effect of one or both Ribeye gene products on the structure of photoreceptor and hair cell ribbons. In Aim 3, we will look at the effect of Ribey removal on the distribution and localization of other synaptic ribbon proteins. In Aim 4, we will investigate the effects of Ribeye loss on exocytosis and calcium current in neuromast hair cells. Understanding synaptic ribbon function at the molecular level will ultimately aid in understanding how visual and auditory information is processed and communicated. In addition, it may provide clues to help understand diseases that specifically affect vision and hearing. In addition, the fundamental understanding of presynaptic processes in these specialized neurons will have broader implications for neuronal communication in general and thus, may contribute to our understanding of various aspects of mental health and neurological disorders.